1. Technical Field
The present invention relates generally to an improved data processing system, and in particular the present invention provides a clock system for use in a data processing system. Still more particularly, the present invention provides a method, apparatus, and computer instructions for generating a set of virtual clocks within a logically partitioned data processing system.
2. Description of Related Art
A logical partitioning (LPAR) functionality within a data processing system (platform) allows multiple copies of a single operating system (OS) or multiple heterogeneous operating systems to be simultaneously run on a single data processing system platform. A partition, within which an operating system image runs, is assigned a non-overlapping sub-set of the platform's resources. These platform allocable resources include one or more architecturally distinct processors with their interrupt management area, regions of system memory, and I/O adapter bus slots. The partition's resources are represented by the platform's firmware to the OS image.
Each distinct OS or image of an OS running within the platform is protected from each other such that software errors on one logical partition cannot affect the correct operation of any of the other partitions. This is provided by allocating a disjoint set of platform resources to be directly managed by each OS image and by providing mechanisms for ensuring that the various images cannot control any resources that have not been allocated to it. Furthermore, software errors in the control of an operating system's allocated resources are prevented from affecting the resources of any other image. Thus, each image of the OS (or each different OS) directly controls a distinct set of allocable resources within the platform.
Some resources, however, might be shared globally between a set of partitions. One such resource is the clock system on the platform. Each OS environment in a set of partitions also frequently requires a clock, which is distinctly different from those used in other partitions. Thus, each partition can require a virtual clock with a specific date/time basis (i.e. a time zone, or a time advance, or lag) which is peculiar to its own environment. It would be advantageous to have an improved method, apparatus, and computer instructions for implementing such a service within a single platform clock subsystem.